thesaurus

A publication that provides synonyms (and sometimes antonyms and other semantic relations) for the words of a given language.

"Roget" is the leading brand name for a print English thesaurus that lists words under general concepts rather than just close synonyms.

As reference books go, the thesaurus has had a somewhat checkered history, in fact, and has probably occasioned as much bad writing as good.

A dictionary or encyclopedia.

A hierarchy of subject headings: canonical titles of themes and topics, the titles serving as search keys.